Why Does 'Operation not allowed after ResultSet closed' Occur When Reusing a Statement Connection in Java?

Closing the ResultSet Before Reusing Statement Connection

In Java database programming, it's occasionally encountered an exception that arises when using a prepared statement after closing the ResultSet. This exception, "Operation not allowed after ResultSet closed," arises specifically when the same connection object is used.

In the given code snippet, a new prepared statement is created using the same connection object after closing the existing ResultSets (rs and rs2). This raises the exception. To resolve this issue and reuse the statement connection, it's best practice to first ensure that all previous ResultSets associated with the Statement are closed.

One recommended approach is using a try-with-resources block, which automatically closes ResultSets and Statements. Here's an example:

try (
    Statement statement = connection.createStatement();
    ResultSet rs = statement.executeQuery("SELECT `name` FROM `user` WHERE `id` = " + userId + " LIMIT 1;")
) {
    if (rs.next()) {
        // Process the results
    }

    try (
        ResultSet rs2 = statement.executeQuery("SELECT `id` FROM `profiles` WHERE `id` =" + profId + ";")
    ) {
        String updateSql = "INSERT INTO `blah` ...";
        PreparedStatement pst = (PreparedStatement) connection.prepareStatement(updateSql);

        while (rs2.next()) {
            // ...
        }

        pst.executeBatch();
    }
} catch (SQLException e) {
    e.printStackTrace();
}

In this example, both rs and rs2 are closed within their respective try blocks before attempting to use the Statement for preparing a new batch. This ensures that there are no open ResultSets before executing the prepared statement.

Remember, maintaining active ResultSet objects is crucial for correct database interaction. Always prioritize proper resource handling and cleanup to avoid exceptions and ensure data integrity.

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